Class Notes NCERT Solutions for CBSE Students
Question: What do you mean by acceleration due to gravity?
Answer: When an object falls freely towards the surface of earth from a certain height, then its velocity changes. This change in velocity produces acceleration in the object which is known as acceleration due to gravity denoted bu letter g . The value of acceleration due to gravity is g= 9.8 m/s2.
Question: What are the differences between the mass of an object and its weight?
Answer:
Question: Why is the weight of an object on the moon 1/6th its weight on the earth?
Answer:
The mass of moon is 1/100 times and its radius 1/4 times that of earth. As a result, the gravitational attraction on the moon is about one sixth when compared to earth. Hence, the the weight of an object on the moon 1/6th its weight on the earth.
Question: Why is it difficult to hold a school bag having a strap made of a thin and strong string?
Answer:
It is difficult to hold a school bag having a thin strap because the pressure on the shoulders is quite large. This is because the pressure is inversely proportional to the surface area on which the force acts. The smaller is the surface area; the larger will be the pressure on the surface. In the case of a thin strap, the contact surface area is very small. Hence, the pressure exerted on the shoulder is very large.
Question: What do you mean by buoyancy?
Answer: The upward force exerted by a liquid on an object that is immersed in it is known as buoyancy.
Question: Why does an object float or sink when placed on the surface of water?
Answer:
- An object sink in water if its density is greater than that of water.
- An object floats in water if its density is less than that of water.
Question: You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
Answer: When we weigh our body, an upward force acts on it. This upward force is the buoyant force. As a result, the body gets pushed slightly upwards, causing the weighing machine to show a reading less than the actual value.
Question: You have a bag of cotton and an iron bar, each indicating a mass of 100 kg when measured on a weighing machine. In reality, one is heavier than other. Can you say which one is heavier and why?
Answer: The cotton bag is heavier than the iron bar. The cotton bag experiences larger up thrust of air than the iron bar. So, the weighing machine indicates a smaller mass for cotton bag than its actual mass.
